Existing multi-frequency wireless devices (e.g., radios) use an antenna structure that attempts to radiate at optimum efficiency over the entire frequency range of operation, but can really only do so over a subset of the frequencies. Due to size constraints, and aesthetic design reasons, an antenna designer may be forced to compromise the performance in some of the frequency bands. An example of such a wireless device could be a mobile telephone that operates over a range of different frequencies, such as 800 MHz to 2200 MHz. The antenna will not radiate efficiently at all frequencies due to the nature of the design, and the power transfer between the antenna, the power amplifier, and the receiver in the radio can vary a considerable amount.
Additionally, an antenna's performance can be impacted by its operating environment. For example, multiple use cases exist for radio handsets, which include such conditions as the placement of the handset's antenna next to a user's head, in the user's pocket, the covering of an antenna with a hand, a pull-out antenna in the up position or down position, a flip phone with the lid open versus closed, hands-free operation with a Bluetooth headset or speakerphone feature, or other operational possibilities, all of which can affect the wireless device antenna's radiated efficiency.
Many existing radios use a simple circuit composed of fixed value components that are aimed at improving the power transfer from power amplifier to antenna, or from the antenna to the receiver, but since the components used are fixed in value there is typically a compromise when attempting to cover multiple frequency bands and multiple use cases.
Prior art systems have attempted to solve this problem by employing a variety of tunable elements in the radio frequency path, thus attempting to compensate for changing antenna performance. Typically, prior art system arrange these adjustable elements into single device substrates or semiconductor die, both to re-use control and bias circuitry between several tunable capacitors on the same die and to reduce the number of input/output connection pads necessary to connect the devices to external circuitry.